Eliminating undesirable rheological properties of legacy waste sludge

Recent research has shown that adding 0.5 vol% colloidal silica (~100 nm) can eliminate the yield stress of a 35 vol% alumina suspension (particle size ~550 nm; yield stress in absence of silica > 100 Pa). Due to the difference in particle size and particle density, the number ratio of the major and minor particle is approximately 1:5. It is hypothesized that elimination of suspension yield stress is via the lubricating action of the spherical additive, and through appropriate particle selection and design of the blending protocol it is envisaged that the blend ratio can be significantly reduced such that the additive has little impact on the overall waste volume.



Research aim: Demonstrate the approach of additive blending to eliminate the yield stress of high solids content legacy sludges.



Research objectives:

Characterize representative test sludges to understand variation in particle size, density, shape and particle/surface chemical composition. This work is crucial to understand the heterogeneous nature of test simulants that mimic sludges encountered in nuclear waste processing. The data will be used to inform of potential particle-types (of differing chemical composition) which could be used as an additive particle.

Test appropriate additive materials to eliminate yield stress of high solids content sludges. Previous research has shown the best performance is achieved when the major and minor component particle species are electrostatically repulsive, however the size difference between the major and minor component species has not been studied. The effect of particle size ratio between the major and minor component species will be considered, along with blending bi-disperse additives to treat polydispersed suspensions.

Study the long-term aging effects of particle additives on the stability, consolidation and rheology of high solids content suspensions. With the plan for legacy wastes to be stored for several decades, it is important that the physical properties of the suspension can be predicted over such time scales. To simulate long-term aging, suspensions with particle additives will be exposed to elevated conditions (centrifugation, temperature, aqueous pH and conductivity) to assess the possibility for the suspension yield stress to redevelop.

Develop the particle additive blending protocol so that the method can be easily scaled. Effective yield stress reduction is achieved when the particle additive is homogenously distributed throughout the yield stress sludge. Methods of adding the particle additive and mixing the particle additive into the yield stress sludge will be studied to demonstrate methods that require little energy and short time effect.

Scale-up the lab-scale method to pilot-plant scale (led by Sellafield Ltd. in partnership with NSG Environmental Ltd.). Working with project partners we will work to translate knowledge from the 100 mL to 500 L scale. Sample preparation and blending protocols will be revisited and optimized for large scale blending.

Project outputs. The research will be communicated with particle partners, industry experts and the wider academic community through reports, presentations and publications. The research student will engage with the relevant Sellafield CoE and work with industry experts to ensure knowledge transfer.

In GREEN we envisage there are potentially Impacts in several domains: the nuclear Sector; the wider Clean Growth Agenda; Government Policy & Strategy; and the Wider Public.

The two major outputs from Green will be Human Capital and Knowledge:

Human Capital: The GREEN CDT will deliver a pipeline of approximately 90 highly skilled entrants to the nuclear sector, with a broad understanding of wider sector challenges (formed through the training element of the programme) and deep subject matter expertise (developed through their research project). As evidenced by our letters of support, our CDT graduates are in high demand by the sector. Indeed, our technical and skills development programme has been co-created with key sector employers, to ensure that it delivers graduates who will meet their future requirements, with the creativity, ambition, and relational skills to think critically & independently and grow as subject matter experts. Our graduates are therefore a primary conduit to delivering impact via outcomes of research projects (generally co-created and co-produced with end users); as intelligent and effective agents of change, through employment in the sector; and strong professional networks.

Knowledge: The research outcomes from GREEN will be disseminated by students as open access peer reviewed publications in appropriate quality titles (with a target of 2 per student, 180 in total) and at respected conferences. Data & codes will be managed & archived for open access in accordance with institutional policies, consistent with UKRI guidelines. We will collaborate with our counterpart CDTs in fission and fusion to deliver a national student conference as a focus for dissemination of research, professional networking, and development of wider peer networks.

There are three major areas where GREEN will provide impact: the nuclear sector; clean growth; Policy and Strategy and Outreach.

the nuclear sector: One of our most significant impacts will be to create the next generation of nuclear research leaders. We will achieve this by carefully matching student experience with user needs.

clean growth - The proposed GREEN CDT, as a provider of highly skilled entrants to the profession, is therefore a critical enabler in supporting delivery of both the Clean Growth agenda, Nuclear Industry Strategy, and Nuclear Sector Deal, as evidenced by the employment rate of our graduates (85% into the sector industry) and the attached letters of support.

Policy and Strategy: The GREEN leadership and supervisory team provide input and expert advice across all UK Governments, and also to the key actors in the nuclear industry (see Track Records, Sections 3.3 & 5.1, CfS). Thus, we are well positioned to inculcate an understanding of the rapidly changing nuclear strategy and policy landscape which will shape their future careers.

Outreach to the wider public: Building on our track record of high quality, and acclaimed activities, delivered in NGN, GREEN will deliver an active programme of public engagement which we will coordinate with activities of other nuclear CDTs. Our training programme provides skills based training in public and media communication, enabling our students to act as effective and authoritative communicators and ambassadors. Examples of such activities delivered during NGN include: The Big Bang Fair, Birmingham 2014 - 2017; British Science Week, 2013 - 2017; ScienceX, Manchester; 2016 - 2018; and The Infinity Festival, Cumbria, 2017.